Glutathione S-transferases (EC 2.5.1.1B) are a class of enzymes involved in the detoxification of xenobiotics. These enzymes are ubiquitous to most living organisms, including microorganisms, plants, insects, and animals. Each gluthatione S-transferase (GST) enzyme within this class is distinct; however, the enzymes do exhibit some overlapping substrate specificity. Jakoby et al., "Rat Glutathione S-transferases: Binding and Physical Properties," in Glutathione Metabolism and function, edited by I. Arias and W. Jakoby (Raven Press, New York, 1976); Reddy et al., "Purification and Characterization of Individual Glutathione S-Transferase from Sheep Liver," Archives of Biochem. and Biophys., 224:87-101 (1983).
Of the multiple GST functions, GST's catalysis of the conjugation of glutathione to electrophilic compounds is of particular interest. H. Rennenberg, "Glutathione Metabolism and Possible Biological Roles in Higher Plants," Phytochemistry, 21:2771-2781 (1982); Meister and Tate, "Glutathione and Related Gamma-Glutamyl Compounds: Biosynthesis and Utilization," in Ann. Rev. Biochem., 45:560-604 (1976). Many xenobiotics, including herbicides, pesticides, and insecticides are electrophilic compounds. In the conjuation of the glutathione and the electrophilic center of the compound, the sulfhydryl group of glutathione reacts with the electrophilic center of the compound. Glutathione participates as a nucleophile by conjugation with the electrophile compound. This conjugation is catalyzed by a specific GST enzyme. (Rennenberg, supra).
In plants, this reaction is important as it provides a mechanism for detoxification of the xenobiotic compound. The conjugated electrophilic, xenobiotic compound is rendered water-soluble and non-toxic to the plant.
It would therefore be desirable to develop plants that are tolerant to herbicides by increasing the levels of glutathione S-transferase enzymatic activity in said plants using genetic engineering techniques. In such a manner, it would be possible to confer herbicide tolerance to a plant.